The present invention relates generally to top opening doors and more particularly to top opening doors for a trailer or the like having a full 270.degree. range of opening movement.
Top opening doors for trailers are well known in the art. U.S. Pat. No. 2,979,361 to Eppinger et al discloses a pair of top covers for a trailer that open over respective sides thereof. When closed, the covers meet along the mid line of the trailer securing the load. The covers, however, are manually operated and very cumbersome. Each cover requires two pivoting connecting links at each end thereof to support their entire weight during movement through 90.degree. from a fully closed to a fully opened position. Further, as disclosed, the covers do not rest upon the box or trailer and thus are not operative to seal the interior of the trailer. Therefore, the covers can allow air to enter the trailer especially at the front, thus causing an increase in internal pressure tending to make the covers lift and fly off. This structural feature makes these prior art covers unsuitable for use on a high speed vehicle.
U.S. Pat. No. 3,854,771 to Anderson is drawn to a one piece cover or door for a trailer top. The door is mounted on roller carriages that roll along the top flanges of the box or trailer. The door may be manually rolled sideways on the roller carriage until it can be tilted downwardly to fully open the top. Often, however, the loading of material leads to matter collecting in the flanges along the top of the trailer, thereby impeding the operation of the door closing function.
U.S. Pat. No. 3,861,737 to Kirkbride discloses a pair of cooperating covers for a trailer top. A chain drive and motor is used to open and close the covers through 90.degree. over respective sides of the trailer. Each cover, however, is carried by a U-shaped carrier having arms at each end. Such an arrangement is unsuitable for modern, extended length trailers for carrying large loads. Also, it is generally recognized that covers of this design would not stand up to rough use without some additional reinforcement of the supporting arms.
A problem common to all of the above prior art is the substantial obstruction created when the doors are open. The doors extend outward from and/or above the trailer creating a hinderance to efficient loading. Additionally, in both Eppinger '361 and Kirkbride '737, separate arms are provided to carry the entire weight of the doors. The lack of additional supporting structure, such as a pivot mounting, leads to inevitable failure of the door opening mechanism when subjected to heavy use. In Anderson, roller carriages are used to support the door. The rollers of these carriages, however, are susceptible to clogging and binding from the dirt and debris associated with the trailer load. Thus, there is a need for top opening trailer doors that do not hender trailer loading when open; and doors of improved durability providing smooth and efficient operation while requiring little or no maintenance.